The working environment for many polymers requires attachment of desirable molecules to the polymer (then acting as a substrate). Particularly in the field of biomaterials, many conventional polymers proposed as biomaterials lack the ability to properly interact with or support biological material, which leads to undesirable biological responses.
It has become recognized that cellular behaviour is determined by the local microenvironment. The cellular microenvironment consists of cell-cell contacts, soluble signalling molecules and an interconnected network of macromolecules known as the extra cellular matrix (ECM), and provides three major categories of physico-chemical signalling; chemical, topographical and mechanical. Chemical signalling from the microenvironment is mediated by membrane proteins (predominantly integrins, but also cadherins, cell adhesion molecules (CAM's) and selectins) that link the cell to the proteins of the ECM and to other cells. Chemical signalling from the ECM is incredibly complex and has been shown to regulate many cellular processes, including proliferation and differentiation. Cells not only respond to the chemical composition of the ECM but also the spatial location of adhesive sites, the surface structure presented to the cell, and the mechanical properties of the matrix.
Whilst many polymeric biomaterials (such as poly(glycolic acid), polylactic acid) and their copolymers, poly(ε-caprolactone), polyurethanes, etc) have been used in an attempt to mimic the ECM, their inherent characteristics, however, limit their suitability for the controlled attachment and subsequent growth of cells and tissues. Their hydrophobic nature, in fact, leads to the adsorption of a non-physiological layer of (mostly denaturated) protein on their surface, further leading to uncontrollable cell-biomaterial interactions and cell responses. It is important in biomaterials applications to eliminate these interactions in favour of tailored biochemical communications with cells via surface-localised peptide or protein signals. It is therefore desirable in many cases to tailor the surfaces of biomaterials to be bioactive, so they can interact favourably with proteins and cells, for instance promoting cell attachment, proliferation, differentiation and ultimately tissue regeneration.
Surface modification is a widely adopted method because it can enhance biofunctionality, tribological properties, and the biocompatibility of a material surface, while keeping the bulk properties intact. In general, the aims of surface modification of biomaterials are to overcome non-specific protein adsorption in vivo, precision immobilization of signalling groups on surfaces, the development of synthetic materials with controlled and tailored properties for drug and cell carriers, biologically inspired materials that mimic natural processes, and the design of sophisticated 3D architectures to produce well-defined patterns for developing bioMEM devices, bioassays, and tissue engineering scaffolds.
Undesirable cellular responses may be controlled by altering the chemical and/or physical properties of the surface of the polymer material. Thus, polymer films can be tailored for specific applications (e.g. tissue engineering) by modification of their surfaces. These techniques include plasma treatments, ion-discharge, surface grafting and wet chemistry methods. Thus, surface modification has become an increasingly popular method of improving biocompatibility and biofunctionality of biomaterials.
While a number of methods exist to functionalise surfaces of polymers (eg those often used in traditional cell culture), many are limited in their capacity to; (i) modify two and three dimensional constructs to an equal extent on all surfaces available to cells; (ii) present multiple bioactive molecules; and (iii) control the spatial location of bioactive molecules. Thus, there is a need to address these limitations.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.